A multi-phase converter comprises a plurality of switching circuits coupled in parallel with each other to satisfy a demand of high load current. In order to optimize the efficiency of the multi-phase converter, auto phase shedding is usually required. In phase shedding mode, a number of switching circuits under power operation is determined by a magnitude of the load current. When the load current is small, only part of the switching circuits are under power operation and transfer power to a load. Once the load reduces, the number of the switching circuits under power operation will reduce. However, due to delay of control, a large undershoot will happen on an output voltage of the multi-phase converter.